The present invention relates generally to a horn switch, and more particularly, to a membrane horn switch for use with a deployable air bag in a vehicle.
This invention relates to a membrane horn switch for use with a driver side supplemental inflatable restraint (SIR) system. Driver side SIR systems typically include an air bag stored in a housing module. These systems are designed to actuate in response to an activation signal in order to rapidly deploy an air bag. A driver side SIR system is normally positioned under a cover within a hub of a steering wheel. In addition, a horn activating switch is also positioned in the same area.
SIR systems are designed such that an inflating air bag cushion is forced out through a cover on the steering wheel in a predetermined manner through a cover tear seam. Because of the location of the horn switch, the switch also has to be designed to accommodate the deploying air bag.
Membrane horn switches require some form of a rigid base to be compressed against. Having the SIR system and the membrane horn switch located within the steering wheel hub calls for the components that make up the SIR system and the membrane horn switch to be tightly packed. When the membrane horn switch is tightly packed between a folded air bag cushion and the steering wheel cover, it may be susceptible to inadvertent actuation. This inadvertent actuation could occur with a minor accidental bumping of the steering wheel cover or with a temperature related compression on the steering wheel cover caused by the expansion or contraction of the integrated parts due to extremes in temperature.
For example, and when the temperature is very cold the steering wheel cover could contract without any pressure exerted on it by the vehicle driver. The temperature related contraction of the steering wheel cover would therefore cause the switch to react in the way it responds when the driver exerts pressure on the steering wheel cover. Accordingly, the horn will sound because the conductive surfaces on the substrate and the flexible membrane are forced together to complete the horn circuit. However, unlike actuation of the horn by hand pressure, the contraction that takes place due to the extreme cold temperature causes the horn switch to remain in the contracted position in which the conductive surfaces are in contact until the temperature rises causing the cover to expand to its original position in which the conductive surfaces are separate from one another. This results in the constant sound of the horn in cold temperatures.
Another consideration in designing membrane horn switches is the amount of pressure needed to actuate the membrane horn switch. It is therefore desirous to have a membrane horn switch that can be activated with a consistent minimal pressure. However, orienting the conductive surfaces close together as is needed for minimal contact actuation also has the added risk of the unintentional closing of the circuit or sounding of the horn.
It is therefore desirable to provide a dual contact membrane horn switch assembly that when exposed to extremes in temperature will not trigger actuation of the switch and thereby sound the vehicle""s horn. In addition, it is desirous to provide a dual contact membrane horn switch assembly which requires consistent minimal pressure to close the circuit and thereby actuate the vehicle""s horn.
A membrane horn switch is provided. The membrane horn switch is for use in a vehicle having a driver side air bag positioned between a steering wheel and an air bag cover. In an exemplary embodiment, the membrane horn switch comprises a top nonconductive sheet with an electrically conductive coating on a bottom surface thereof, a bottom nonconductive sheet having an electrically conductive coating on a top surface thereof, and a nonconductive spacer disposed intermediate the top and bottom nonconductive sheets.
Defined within the top, bottom and nonconductive spacer sheets are a first main switch section and a second main switch section. A bridging section selectively interconnects the first main switch section and the second main switch section. The bridging section includes a bridging tear seam extending between the first and second main switch sections. The membrane horn switch also further includes a pair of electrical leads disposed within the structure such that the pair of leads intersect the bridging tear seam and serve to connect the horn membrane switch to an actuation device (e.g. a horn) so that deployment of the air bag causes the horn membrane switch to be separated because the bridging tear seam is torn resulting in the leads also separating to interrupt a circuit of the horn membrane switch. This results because the bridging tear seam is preferably aligned with the tear seam of the air bag so that deployment of the air bag causes both seams to rupture and sever the tear seam.
Thus, the membrane horn switch is designed so that both hot and neutral leads of the membrane horn switch which connect the switch and the vehicle""s horn are located across the tear seam of the switch so that upon deployment of the air bag the bridging tear seam and the switch leads are severed.
A membrane horn switch assembly designed so that a steering wheel cover can expand or contract due to extremes in temperature without the unintentional closing of a circuit used to activate a remote horn. Also, the assembly includes a membrane horn gap which is designed so that the space between the cover or reaction plate concentrators and the switch is minimized thereby requiring less pressure exerted on the steering wheel cover to actuate the switch. Additionally, the steering wheel cover is designed so that a greater deflection in the cover results when using the same amount of pressure as was previously exerted on the cover.
In one embodiment, the membrane horn switch assembly of the present invention comprises a membrane horn switch having an upper flexible substrate sheet having a bottom surface coated with a conductive material, a lower flexible substrate sheet with a conductive positive and a negative grid disposed on a top surface thereof and a dielectric spacer interposed between the upper and lower flexible substrate sheets. The dielectric spacer partially defines a predetermined number of points where an electrical connection may be provided between the upper and lower sheets when assembled.
According to one embodiment, the membrane horn switch has a predetermined datum scheme (i.e., pattern of concentrators) to register switch contact points so that the concentrators are properly orientated relative to the conductive positive and negative grids. This method of registration eliminates dielectric interference in the membrane horn switch. Dielectric interference is one cause of malfunctioning of the membrane horn switch due to improper alignment and contact between layers comprising the membrane horn switch. Furthermore, the membrane horn switch assembly also has locating features that further permit the desired registration of the switch contact points.
In addition, the membrane horn switch is designed so that temperature extremes and inadvertent bumping of the steering wheel cover does not result in the unintentional activation of the membrane horn switch.
The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings and appended claims.